A photolithography device is used in the production of three-dimensional structures on semiconductor chips. It is used to expose a photoresist (also called “resist”) applied to a semiconductor chip (“wafer”) to light in a desired manner. Thus the image of a mask is projected onto the photoresist which is exposed to light differently by reason of the casting of a shadow. The exposure causes the photoresist to change its physical and/or chemical properties so it can subsequently be removed e.g. in a selective manner.
The light used to expose the photoresist is provided by a light source which comprises a plurality of LEDs. Thus different LEDs can be used which provide light with different specific wavelengths (or wavelength ranges).
However, it has proved to be the case that the LEDs age differently depending on the wavelength of the light they provide. The result of this is that the distribution of the light output provided by the light source over the spectrum changes over time. Therefore, the exposure result in the photoresist changes depending on the age of the LED light source, i.e. with the age of the exposure assembly.
It is the object of the invention to ensure that the spectrum of the exposure assembly, i.e. the intensity distribution of the different wavelengths of the exposure assembly, is kept constant over time.